The present invention relates to a device for the purification of blood comprising a blood extraction conduit, a blood return conduit, blood filtration means located between the extraction conduit and the return conduit, means to circulate the blood, an evacuation conduit for the liquid from said filtration means called the ultra-filtrate, means to circulate the ultra-filtrate in said evacuation conduit, a source of substitution solution, a connection conduit between this source and said blood extraction conduit, pre-dilution control means to circulate the substitution solution, means for measuring at least one parameter influenced by the resistance of the filtration means to the flow of the liquid, and a computation unit.
The extra-corporeal purification has for its object on the one hand to clean the blood of patients by withdrawing undesirable elements and on the other hand controlling the weight of the patients. The invention is applicable most particularly to hemo-filtration which is distinguished from dialysis by the fact that the purification takes place by convection rather than by diffusion through a semi-permeable membrane. In the two cases, the operator is required to intervene during the sessions, in particular to avoid coagulation in the extra-corporeal circulation conduit, which takes place particularly at the filter.
The coagulation of extra-corporeal circulation during hemo-filtration is conventionally reduced by using anticoagulants (heparin, liquemin) and by proceeding at regular intervals to rinse the circuit and change the filters.
Although often well tolerated by patients at conventional dosages, the use of anticoagulants is contraindicated in certain cases, for example for patients having substantial lesions.
As to rinsing, this is an operation which consists in causing the physiological liquid to circulate instantaneously in the filter in place of the blood. This takes place by obstructing the blood extraction conduit with a clamp, connecting a pouch of physiological liquid to the blood extraction conduit, making sure that a sufficient quantity of physiological liquid has flowed, conventionally 100 to 300 ml. This quantity is considered as suitable to clean the filter. The previous flow conditions are then reestablished to continue the treatment. This sequence of operations takes a long time and can lead to handling errors. Moreover, it interrupts the treatment and the operator must take account of the surplus of liquid injected into the patient when calculating the hydric balance of the patient.
In the case in which a change of the filter is necessary, it is necessary to return his blood to the patient, rinse the new filter, then continue the treatment. This operation is long and costly and should therefore be avoided whenever possible.
It should also be noted that, to the phenomenon of coagulation, there is also that of clogging, which is a deposit of molecules on the extra-corporeal circulation surfaces and particularly the filter walls. This clogging also reduces the capacity for blood purification and is eliminated in the same way as coagulated deposits. In what follows of this specification there will be used indiscriminately the terms coagulation or clogging to designate these two phenomena.
It was proposed in WO 83/04373 to provide an apparatus for automatically carrying out rinsing by actuating electromechanical clamps at predetermined time intervals, by the operator. EP 0 235 591 proposes adding a clamp which permits varying the pressure in the filter so as to increase the rinsing effect. The drawback of these two solutions resides in the fact that the rinsing is decided by the user who has only an approximate idea of the speed of coagulation of the system. As a result, either the rinsing is too frequent, which decreases the effectiveness of the treatment by repeated interruptions of the treatment, or else it is not frequent enough, leading to coagulation by insufficient rinsing.
WO 98/50091 describes a process for controlling an extra-corporeal blood purification device, this latter comprising a blood extraction conduit, a blood return conduit, blood filtration means, means to circulate the blood, an evacuation conduit for ultra-filtrate from said filtration means, means to cause the ultra-filtrate to circulate, a source of substitution solution, a connection conduit between this source and the blood extraction conduit, a means to cause the substitution solution to circulate in this connecting conduit. This device also comprises a computation unit and measuring means which can permit determining at least one parameter influenced by the resistance of the filtration means to the flow of liquid. The process disclosed in this document permits such an apparatus moreover to compare the measured parameters with threshold values, control means applying new reference values to reduce the difference between the value of the measured parameter and the threshold value. This process is however limited to the good operation of the apparatus as to its principal functions, which is to say to regulate the circulation of the fluid in the two circuits of the apparatus and particularly to balance the extracted and substituted masses. No reference is made to a solution to avoid or actively remove coagulation of the blood by using the process or the device proposed in this document.
It is to be noted that the exchange volume, to which corresponds an exchange flow rate, is defined as being the volume of liquid taking part in purification of the blood withdrawn from this latter in the course of the session. If there is no loss, particularly by pre-dilution, this volume corresponds to that of the ultra-filtrate. This is the quantum which, in hemo-filtration, determines the degree of purification of the blood in the course of the session, which can also be defined as being the quantity of impurities withdrawn from the blood.
None of the systems described above is really satisfactory, because they are not adaptable to variations in the operating parameters which can arise during the treatment. Moreover, the patients are regularly purified in an insufficient manner because the prescribed volumes are calculated by assuming that all the substitution liquid is injected with post-dilution, the values not being corrected to take account of the proportion of this liquid introduced by pre-dilution.
The physical parameters which can have an influence on the coagulation of the system are numerous. There can be particularly cited the material and the surface of the filter, the blood composition and flow rate, the dosage of anticoagulant prescribed and the desired exchange flow rate. These parameters can vary in the course of the treatment in important ways and at short intervals. It is thus impossible for the user to control the condition of the system so as to avoid systematically its coagulation. This is all the more true when the duration of the treatment can be several days and the exchange flow rates are great, for example 12 liters per hour.
The object of the present invention is to overcome at least in part the above-mentioned drawbacks.
To this end, this invention has for its object an extra-corporeal blood purification device of the type mentioned above.
An essential advantage of this invention resides in the fact that this device does not require the intervention of the user during the treatment.
The device according to the invention permits minimizing the substitution solution consumed and adapting the exchange volume so as to observe, to the extent possible, all the standards required by the user.